1. Field of the Invention
The present invention relates to a solid-state imaging device used in video cameras or the like and having optical component parts such as color filters, microlenses, etc. directly formed on a semiconductor substrate, and to a method of manufacturing the same.
2. Description of the Prior Art
In recent years, there has been an increasing need for reduction in size and enhancement of performance in the field of video cameras and other apparatus, and to meet such needs, efforts have been directed to the development of further miniaturized, higher sensitivity solid-state imaging devices which are used in such apparatus. For miniaturization and enhanced sensitivity of a solid-state imaging device, optical component parts such as color filters and microlenses are formed directly on a semiconductor substrate on which the solid-state imaging device is formed.
Formation of such optical component parts, for example, microlenses, is accomplished in the following manner. First, a transparent, non-dyeable material such as acrylic resin, epoxy resin, polyimide resin, etc. is applied by spincoating on a semiconductor substrate with a plurality of solid-state imaging devices formed thereon, thereby smoothing the surface of the semiconductor.
Thereafter, a dyeable resist for forming filters, such as gelatine, casein, etc. is applied also by spincoating, exposed to light, and developed to form a dyeable resist pattern on the pixel regions. Next, the resist pattern is dyed with a dyestuff having a desired spectral characteristic to obtain a color filter pattern. The process is repeated several times to form on-chip color filters.
On the substrate processed in this way, the same material as used for smoothing the substrate surface is applied, also by spincoating, to form a flat protective film, and on top of the protective film are formed microlenses, one for each pixel, using a known technique such as disclosed in Japanese Laid-Open Patent Publication No. 64-10666. The on-chip microlenses are thus formed.
According to the above method, the non-dyeable material for smoothing the surface, the dyeable resist for forming color filters, and the resist for forming microlenses are applied on the substrate using the spincoating technique. However, since the substrate surface is uneven because of scribe lines, metal wiring, etc. formed therein, films applied by spincoating on the substrate tend to become uneven in thickness because of the irregularities on the substrate surface. For example, FIG. 5 shows a case in which a color filter resist film 33 formed on a substrate 31 has an uneven thickness over the same pixel region. This appears as a thickness variation 32 on the surface of the resist film 33, as shown in FIG. 6. That is, a striation appears. FIG. 5 is a cross section taken along line A--A' in FIG. 6.
When color filters are formed by dyeing such a resist film, the resulting problem is that imaging and sensitivity variations occur and thus the picture quality is substantially degraded, because of the thickness variations of the filter layer portions corresponding to the respective pixels.
In order to enhance the light gathering efficiency of the microlens, it is essential that the thickness of the protective film below the microlens and the thickness of the microlens resist film be maintained uniform. However, because of the irregularities on the substrate surface, as mentioned above, it has been difficult to maintain the thicknesses of the two films uniform. Since the uneven thickness of the microlens resist film leads to uneven spacing between adjacent microlenses and variation in the bottom area thereof, there occurs variation in the light gathering efficiency among the microlenses, which causes sensitivity variations leading to degradation of the picture quality.